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Old 20th October 2011, 07:38 AM   #341
qusp is offline qusp  Australia
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yes, it will be really quite interesting putting the NTD1 (opc) (only the mosFETs, caddock to220, TX220Z zfoils and auricap/vcap CuTF in the signal) against the SEN/CEN. They are 2 simple (although in the rather extreme case of the NTD1 it requires serious commitment due to size and heatsinking) and both are circuits with very few parts and a rather pure modus.

NTD1 measures about 15db better in THD+N in this form, but i'm looking for sonics, which are superb on the NTD1, so something smaller/less awkward that approaches or equals but slightly different is what i'm after for the tweeter dac. i'm not looking to replace the D1, so the comment of people unhappy with their sabre IV stages doesn't hold for me. I'm using one of several choices including the SEN/CEN to run the DAC->AMP->tweeters section of my system, with the NTD1 running the mid bass->mid.

Last edited by qusp; 20th October 2011 at 07:40 AM.
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Old 20th October 2011, 11:00 AM   #342
regal is offline regal  United States
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Quote:
Originally Posted by EUVL View Post
Guess this is what Calvin was referring to :

Easy-to-build I/V stage


Patrick
He said improved Jocko, I believe that is the non-improved Jocko.


I guess my issue with J-fet designs is the high input impedance. Reports are coming in good with the Cen using the PCM1704, a chip which I have dived deep into and know that it is adding significant distortion with less than a 10 ohm load.

All I am saying is if the PCM1704 sounded good with this high of an input impedance I/V, the Cen must be pretty damn good. But probably a better match for PCM56/58/63 which aren't as touchy.
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Old 20th October 2011, 11:03 AM   #343
EUVL is offline EUVL  Europe
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> He said improved Jocko

Please post a link for the benefit of all.


Thanks,
Patrick
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Old 20th October 2011, 11:17 AM   #344
Calvin is online now Calvin  Germany
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Hi,

actually I was referring to a simpler Jocko as in the attachment. I called it ŽimprovedŽas the THD-values for this simple version were reported to be less good, possibly not better than -60dB at 0dBfs.
Indeed fell the first testands into that range and I started to tune and tweak. Now my versions are consistant at -90dB and better (measured at the output of the associated JFET-bufferstage and 0dBfs).
The CCS towards the positive supply is omitted with and the Riv is used instead.
C1 limits the bandwidth. In conjunction with C2 the input impedance of the circuit may be linearized up into the MHz range.
J1 is a simple NJFET-current sink. Its current taking over the DACs offset current plus the bias current of Q1a. Its bias may be tuned by P1, thereby setting the dc-working-point at the same (influence on THD-values too). C3 blocks dc and couples the audio signal to the following (buffer-)stage. If R3 is rather large in value as it could be as the Gate-resistor of a JFET-bufferstage, C3 may be small in value (and size). The current through Q1 is set by the value of R2. Tuning of R2 allows to null the input offset at Q1aŽs emitter.
The quality of the supply voltages needs to be high, since the positive PSRR is low. But then we need quality supplies in audio anyway. ;-)
Against the before linked Jocko with its two bipolar CCS setting the working points is very easy and the circuit is lower in noise (and seemingly also lower in THD).
The circuit resembles certain similarities to the D1 and OPCs Power-MOSFET version of the D1, but requires less effort regarding power consumption, heat dissipation, size, high values of supply voltages, sourceability of parts and cost. Using easy to source matched dual transistors no further matching is required. A solder station and a DVM to control the dc-working point is all whats needed to get the thing running.

jauu
Calvin
Attached Images
File Type: jpg I-V Jocko principle.jpg (55.9 KB, 638 views)

Last edited by Calvin; 20th October 2011 at 11:40 AM.
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Old 20th October 2011, 11:45 AM   #345
EUVL is offline EUVL  Europe
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Actually same problem as the Pass Zen IV -- no PSRR and coupling cap in voltage mode.
But indeed very simple.


Patrick
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Old 20th October 2011, 01:07 PM   #346
regal is offline regal  United States
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Quote:
Originally Posted by EUVL View Post
Actually same problem as the Pass Zen IV -- no PSRR and coupling cap in voltage mode.
But indeed very simple.


Patrick
Much lower distortion than Pass Zen, much lower input impedance. Zen really measures like a passive I/V+ tube stage but with better S/N.

Coupling cap is a coupling cap, my guess is he probably has a dc coupled buffer figured out.
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Old 20th October 2011, 06:59 PM   #347
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Quote:
Originally Posted by EUVL View Post

As to other circuits.
We have our own version of all.JFET D1, and the Hawsford as you mentioned.
They do not offer any sonic advantages but are much more complicated.
And the CEN / SEN are dead quiet !!!

As said, we use SEN ourselves for PCM1704.


Patrick
Patrick

have you build this I/U stage D1 clone with 2sk389 finetuned...

for me It Is step ahead over original D1 I/V

your comments please
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Old 20th October 2011, 08:19 PM   #348
EUVL is offline EUVL  Europe
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Yes, I am aware of those JFET variants of D1, if that was your question.

Like Joachim Gerhard, rtd & ryanj, it will take you less than an hour to get a breadboard SEN/CEN working.
So why not just try it for yourself ?


Patrick
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Old 21st October 2011, 08:14 AM   #349
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Hi fellas,

Patrick you mention that you use SEN for PCM1704. I currently use Spencers D1 IV on a PCM63 (Balanced) DAC. Did you find the SEN better than the Spencer D1?
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Old 21st October 2011, 08:43 AM   #350
EUVL is offline EUVL  Europe
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I don't have a Spencer D1. I have my own version of a similar all JFET IV which has no coupling cap but split rails.

It has the same input impedance as SEN, but quite a bit more distortion, even though mostly 2nd harmonics.
And it is also more complicated (7 JFETs) and requires a (additional JFET) servo.

So the choice is simple.

There is no point in asking me which sounds better than which.
This is something everyone has to decide for himself.

And the IV is only one component in an entire audio chain.
So I shall not make such comments or statements, except to tell you what we choose for our own use.


Patrick
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